It is conventional practice to provide the cylinder block of an internal combustion engine with numerous cast in place interconnected coolant passages within the area of the cylinder bore. This allows maintaining the engine block temperature at a predetermined acceptably low range, thereby precluding excessive heat distortion of the piston cylinder, and related undesirable interference between the piston assembly and the piston cylinder.
In a conventional diesel engine having replaceable cylinder liners of the flange type, coolant is not in contact with the immediate top portion of the liner, but rather is restricted to contact below the support flange in the cylinder block. This support flange is normally, of necessity, of substantial thickness. Thus, the most highly heated portion of the cylinder liner, namely the area adjacent the combustion chamber, is not directly cooled.
Furthermore, uniform cooling all around the liner is difficult to achieve near the top of the liner because location of coolant transfer holes to the cylinder head is restricted by other overriding design considerations. The number of transfer holes is usually limited, and in many engine designs the transfer holes are not uniformly spaced.
All of the foregoing has been conventional practice in internal combustion engines, and particularly with diesel cycle engines, for many, many years. However, in recent years there has been a great demand for increasing the horsepower output of the engine package and concurrently there exists redesign demands to improve emissions by lowering hydrocarbon content. Both of these demands result in hotter running engines, which in turn creates greater demands on the cooling system. The most critical area of the cylinder liner is the top piston ring reversal point, which is the top dead center position of the piston, a point at which the piston is at a dead stop or zero velocity. In commercial diesel engine operations, it is believed that this temperature at the piston reversal point must be maintained so as not to exceed 400.degree. F. (200.degree. C.). In meeting the demands for more power and fewer hydrocarbon emissions, the fuel injection pressure has been increased on the order of 40% (20,000 psi to about 28,000 psi) and the engine timing has been retarded. Collectively, these operating parameters make it difficult to maintain an acceptable piston cylinder liner temperature at the top piston ring reversal point with the conventional cooling technique described above.